Recognize newly described Polioptila attenboroughi and split Polioptila guianensis into
three species

Effect on SACC: If adopted, this proposal would add a newly described species of Polioptila to the list and recognize two
current subspecies of P. guianensis (paraensis and facilis) as species-level taxa.

Background: Based on
several sight records and tape-recordings and three specimens collected of a
member of the P.guianensis group west of the Rio Madeira, Whittaker et al. (2013) described a new species ofPolioptila,
P. attenboroughi, from the west bank of the Madeira and
south of the Solimões rivers in the Inambari area of endemism (Silva et at.
2005) in Brazil. Analyzes of the tape-recordings and of the collected specimens
indicated that this taxon is phenotypically and genetically distinct from other
taxa in the P. guianensis complex.

Newly
Published information:

Morphology. - Adult males (no female specimens are
available) of the new taxon are readily distinguished from males of all
remaining taxa in the P. guianensis
complex by decisively darker plumbeous upperparts, chest and lower throat, in
these respects approaching P. facilis
and P. schistaceigula (Slate-throated
Gnatcatcher) further differing from the former by a thin, broken, white eye
ring (nearly absent in P. facilis), and
from the latter by a significantly longer tail with white on the outer
feathers, and lack of any white in the head. In comparison with recently
described P. clementsi, it further
differs by the greater extent of black basis on outer rectrices. From P. paraensis, with which the new taxon
shares the tail pattern, differentiated only by a much darker slate color of
the upperparts, throat, and chest (Whittaker et al. 2013).

Voice. - The loudsong of P. attenboroughi is most similar to that of P. paraensis in comprising an evenly paced series of notes at a
nearly level frequency, but pace is significantly slower and note shape (and
thus, auditory quality) is subtly different. Furthermore, P. attenboroughi possesses a distinctive "rasp" series
delivered in the context of a complex song that is lacking, or perhaps only
very rare, in P. paraensis but shared
with P. schistaceigula (Fig. 2 in
Whittaker et al. 2013).

Genetic divergence. - Separated from
its sister-species, P. paraensis, by
approximately 3.9% sequence divergence, and from the more distantly related P. schistaceigula and P. guianensis, respectively, by 14.3%
and 13.6% sequence divergence in the mitochondrial gene NADH subunit 2 (Fig. 3
in Whittaker et al. 2013). The uncorrected p
genetic distance between P. attenboroughi
and P. paraensis (3.9%) is nearly
identical to that reported for a pair of parapatric sister-species of Polioptila in North America (4% for P. californica and P. melanura), and also based on the same gene (Zink and Blackwell
1998).

Analysis/Recommendation: The fact that the phylogenies recoveredP.
attenboroughiandP. paraensis as reciprocally monophyletic taxa with strong statistical support (Fig.
2 in Whittaker et al. 2013), along with their morphological and vocal
differentiation, supports their recognition as valid species-level taxa (De
Queiroz 2007). The English name, Inambari Gnatcatcher, reference the center of
endemism to which the new taxon is restricted. Also, the molecular phylogeny
obtained by Whittaker et al. 2013 showed with
strong support that the Polioptila
guianensis complex is not monophyletic with respect to Polioptila schistaceigula from west of the Andes, reinforcing the
treatment of other taxa currently regarded as subspecies in this complex (paraensis and facilis) as independent species, as supported by Whitney and
Alvarez (2005).

Literature
Cited

De Queiroz, K. (2007). Species concepts and species delimitation.Systematic
Biology56 (6): 879-886.

Whitney, B. M. and J.
Alvarez A. (2005). A new species of gnatcatcher from white-sand forests of
northern Amazonian Peru with revision of the Polioptila guianensis complex. Wilson
Bulletin 117:113-210.

Comments from Remsen: “NO, but based
strictly on a technicality, namely the proposal is framed as if paraensis and facilis are treated as species, which SACC does not – see proposal 204.So, we can’t elevate attenboroughi to species rank without also reconsidering the
critical taxa in this group.Also, as
noted in my comments on similar proposals, discussing “reciprocal monophyly”
with such a small N of individuals is completely inappropriate.Further, comparative genetic distances are
also an inappropriate way to evaluate species limits, especially when
temperate-latitude taxa are compared to isolated tropical ones.That said, the vocal differences portrayed in
the sonograms and described in the text, combined with the plumage differences,
are consistent with species rank for taxa in this group, given that these
differences are comparable to those between taxa treated as species in this
genus, in which morphological divergence is slight.What we need is a comprehensive proposal on
the group, i.e. a revised 204 combined with the current one.”

Comments
from Stiles: “NO.The evidence presented could be sufficient
for recognizing attenboroughi, but
whether as a subspecies or species is uncertain without more data from all
forms of this gnatcatcher complex: in effect, in order to justify splitting all
these forms as species requires more comprehensive data (morphometrics, voice,
genetics) from all of them; also, the painting of attenboroughi fails to show the supposedly diagnostic difference in
tail pattern; photos of representative specimens of all forms showing this (as
well as other characters mentioned) should also be included.”

Comments from Nores: “NO, for the reasons given by Van and
Gary. We can’t elevate attenboroughi
to species rank without also reconsidering the critical taxa in this group. The
evidence presented may be sufficient for recognizing attenboroughi, but whether as a subspecies or species is uncertain.
Discussing “reciprocal monophyly” with such a small number of individuals is
inappropriate.”

Comments
from Zimmer: “YES,
although with more than a little hesitation.I spearheaded the rejection of Proposal 204 (splitting guianensis into 3 species), largely on
the grounds that I felt the sample sizes of audio recordings were tiny (and
with virtually no geographic breadth) for nominate guianensis and facilis,
and, because I felt that the described vocal differences between the three taxa
were subtle relative to those between subspecies-pairs in the plumbea and dumicola complexes (and, because we are dealing with oscine
passerines whose vocal repertoire is at least shaped by learning).The description of attenboroughi has the added advantage of genetic data (but see
caveats by Van, Gary and Manuel in their comments on this proposal), revealing
some pretty large sequence divergences between north-bank guianensis and the clade containing paraensis and attenboroughi.Also, Whittaker et al (2013) fleshes out the
vocal comparison, at least for attenboroughi
and paraensis, although it does
little to make the case for guianensis
and facilis beyond presenting the
genetic data.I have seen and
tape-recorded all four taxa (including attenboroughi),
and I continue to be underwhelmed by the relatively subtle vocal differences
among the 4 taxa in the guianensis
complex, at least when these are placed in the context of vocal differences
between populations of P. plumbea and
P. dumicola that are still considered subspecies despite having
dramatically different songs. As I stated in my remarks on Proposal 204, this
may be less an indictment of recognizing attenboroughi
and splitting guianensis than it is
an argument for splitting up plumbea
and dumicola, but it does mean that
the yardstick approach cannot be used in making the present case.I think that the qualitative (= note shape
and call structure) differences between attenboroughi
and paraensis noted by Bret in his
vocal analysis in Whittaker et al 2013 are likely more significant than the
pace differences in the primary songs, especially given that the songs in these
birds are learned.I am not bothered by
the relatively minor plumage distinctions between the four taxa – plumage
variation within the genus is highly conservative.[Just as an aside, Whittaker et al 2013 describe
the plumage of attenboroughi as being
very saturated, dark gray, “approaching schistaceigula”.This does not square with my experience with schistaceigula from Panama, which is
nearly blackish-gray, and much darker than any of the attenboroughi that I’ve seen (6-8 individuals, including what
appeared to be a family group of 4).It
is possible that the schistaceigula
at the western limit of their range are darker than the South American
populations – if so, then schistaceigula
may also exhibit some geographic structure in vocalizations, making everything
in the complex more complicated than previously thought.]Anyway, I think that Whittaker et al 2013
makes a strong case for recognition of attenboroughi
as a distinct taxon in the guianensis/schistaceigula
complex – it should be recognized at some taxonomic level.I’m on the fence as to whether that level
should be as a distinct species versus a subspecies of a polytypic guianensis, but biogeographic
considerations and the genetic data suggest to me that treating each of the
populations as separate species that are part of a superspecies is probably the
correct course.So, again, a tepid YES.”

Comments from Robbins: “YES. Van makes the point that given how we haven’t
recognized paraensis and facilis (I was on the fence on whether
they should be recognized as a species) that we shouldn’t make a decision on
the status of attenboroughi until we
address the entire guianensis
complex. As at least a couple of us
pointed out in our evaluation of proposal 204, plumage morphology is so subtle
and plastic in this family that in my opinion it has little utility.Moreover, having analyzed literally dozens of
songs both within and across Polioptila
taxa, I would submit that this character also has limited utility in defining
species limits. Thus, given those
limitations, I do consider the genetic data to be very important in assessing
species limits.The fact that attenboroughi is so different from
purported relatives leaves no doubt that at a minimum paraensis and attenboroughi
together should be considered a distinct species from other taxa within guianensis.However, I would go one step further and now
would support recognizing both paraensis
and attenboroughi as species. Of course, if we take that path then I presume
that we should treat clementsi and facilis as species.”

Comments
from Jaramillo: “YES –
this is a tough one, marginal, yet the little information that is out there
seems to be borderline positive to make some decisions. I see the point made by
Van on structure of the proposal (it is not the best argument made there in my
opinion, a bit messy and confusing), but I am following the thoughts by Mark
Robbins. There are characters mentioned in the proposal that are perhaps not
all that useful, but even with the small sample size and limitations the
sequence divergence is large. Adding things up, primarily basing on sequence
divergence, but adding in the morphology and song, I do think that this newly
described species is a good one.”

Comments
from Stotz: “YES I
understand that this only makes sense if facilis
and paraensis are split from guianensis, but I think they should
be. If this were still in question, I might be a little more concerned
about the niceties of doing a proper proposal for facilis and paraensis.
I would encourage a new proposal to split all of these personally, although
reading the comments makes it unclear to me that with the current data, enough
of the committee would be convinced.”